The invention relates to fiber composite structures of elongate irregularly shaped shell body form and to a method for manufacturing such a composite.
Shell bodies having configurations based on barrel-shaped cylinders, frustum of right circular cones, ball (spherical) ellipsoid and parabolic shaped cones, venturi-shaped tubes and combinations thereof with right circular cylinders are extensively utilized as exhaust rocket nozzle and exit cone components. Such shell bodies typically comprise a fiber reinforced composite construction. However, present fiber composites do not display optimum structural properties when put to such use. Rather, present composites exhibit difficulty in withstanding the demanding thermostructural requirements placed upon them. Often, conventional constructions exhibit anisotropic properties, with one direction undesirably weaker than the other.
One present method of providing fabric composites is the involute fabric lay-up technique wherein several bunched plies of fabric previously impregnated with phenolic resin, e.g. prepregged fabric, are laid up on the other support. Each fabric ply typically extends from end to end and the resulting lay-up of fabric plies around the periphery of the support resembles a deck of fanned out playing cards. Following completion of the lay-up considerable debulking of the plies is required to condense the bulk of the layers prior to final molding and curing. During such debulking the fabric plies tend to wrinkle and be distorted. Such defects may cause delamination of the fabric plies in the resulting molded resin composite, subsequent densification processing of the resin base composite into carbon-carbon composite form or failure during propulsion motor test firing. Further, the orientation of the fiber in the fabric plies is such that the construction is inherently weak in the peripheral direction. Warp fibers, which are arranged in an off axis pattern are noncontinuous. Because the fabric plies are distinct the crossing fibers are likewise noncontinuous. Such noncontinuity results in composite weakness in both the longitudinal and peripheral directions.
Several alternative material methods of construction and fabrication approaches including filament winding, braiding, knitting, woven socks and 2D/3D construction have been utilized. However each of these new concepts have inherent deficiencies in their constructions in terms of providing resistance to in-process delamination and an optimum balance of material properties needed for in-use application. Some of the inherent drawbacks of these concepts include; limitation in achieving high fiber content, lack of cross-ply reinforcement to prevent in-process delamination of plies and lack of a mechanism for venting (out-gassing) of volatiles generated between plies during densification process.
It is therefore an object of this invention to provide a fabric composite which exhibits enhanced isotropic structural strength.
It is a further object of this invention to provide such a composite which is suitable for use in complex irregular shaped applications such as for rocket motor components, e.g. rocket exhaust nozzles and exit cones.
A further object of this invention is to provide constructions capable of sustaining fabrication (lay-up and/or molding) processing, resin impregnation and subsequent carbonization and graphitization processing and motor firing survivability without inducing wrinkles, fiber distortion and/or delamination.
A further object of this invention is to provide constructions having flexibility in altering the architecture of reinforcement to meet specific thermostructural design requirements.
It is a further object of this invention to provide a method for constructing the aforesaid composite manufacture.